Role of the direct and indirect pathways for glycogen synthesis in rat liver in the postprandial state
The pathway for hepatic glycogen synthesis in the postprandial state was studied in meal-fed rats chronically cannulated in the portal vein. Plasma glucose concentration in the portal vein was found to be 4.50 +/- 1.01 mM (mean +/- SE; n = 3) before a meal and 11.54 +/- 0.70 mM (mean +/- SE; n = 4) after a meal in rats meal-fed a diet consisting of 100% commercial rat chow for 7 d. The hepatic-portal difference of plasma glucose concentration showed that liver released glucose in the fasted state and either extracted or released glucose after feeding depending on plasma glucose concentration in the portal vein. The concentration of portal vein glucose at which liver changes from glucose releasing to glucose uptake was 8 mM, the Km of glucokinase. The rate of glycogen synthesis in liver during meal-feeding was found to be approximately 1 mumol glucosyl U/g wet wt/min in rats meal-fed a 50% glucose supplemented chow diet. The relative importance of the direct vs. indirect pathway for the replenishment of hepatic glycogen was determined by the incorporation of (3-/sup 3/H,U-/sup 14/C)glucose into liver glycogen. Labeled glucose was injected into the portal vein at the end of meal-feeding. The ratio of /sup 3/H//sup 14/C in the glucosyl units of glycogen was found to be 83-92% of the ratio in liver free glucose six minutes after the injection, indicating that the majority of exogenous glucose incorporated into glycogen did not go through glycolysis. The percent contribution of the direct versus indirect pathway was quantitated from the difference in the relative specific activity (RSA) of (/sup 3/H) and (/sup 14/C)-glycogen in rats infused with (3-/sup 3/H,U-/sup 14/C)glucose. No significant difference was found between the RSA of (/sup 3/H)glycogen and (/sup 14/C)glycogen, indicating further that the pathway for glycogen synthesis in liver from exogenous glucose is from the direct pathway.
- Research Organization:
- National Institute on Alcohol Abuse, Rockville, MD (USA)
- OSTI ID:
- 5208078
- Journal Information:
- J. Clin. Invest.; (United States), Journal Name: J. Clin. Invest.; (United States) Vol. 81:3; ISSN JCINA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
ALDEHYDES
ANIMALS
BIOLOGICAL PATHWAYS
BIOSYNTHESIS
BODY
CARBOHYDRATES
CARBON 14 COMPOUNDS
DIET
DIGESTIVE SYSTEM
ENZYMES
GLANDS
GLUCOSE
GLYCOGEN
HEXOSES
ISOTOPE APPLICATIONS
ISOTOPE RATIO
LABELLED COMPOUNDS
LIVER
MAMMALS
METABOLISM
MONOSACCHARIDES
ORGANIC COMPOUNDS
ORGANS
PHOSPHORUS-GROUP TRANSFERASES
PHOSPHOTRANSFERASES
POLYSACCHARIDES
RATS
RODENTS
SACCHARIDES
SYNTHESIS
TRACER TECHNIQUES
TRANSFERASES
TRITIUM COMPOUNDS
VERTEBRATES